Agreed: for most of my day to day tasks, emacs is performance enough, subject to the constraints of my CPU vis a vis interpreting the underlying lisp...but I do find myself actively avoiding a long line of JSON blob, because of the reliable repeatability of emacs locking up and becoming unusable on a long line.

It’s not enough to stop me using emacs, but it is enough to make me go out of my way to avoid it (and to grumble about).